<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue-2.4.0.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="n1">
        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>
        <input type="text" v-model="n2">
        <input type="button" v-model="result" @click ="ccc">
    </div>
    <script>
        var vm = new Vue({
            el:'#app',
            data:{
                n1:0,
                n2:0,
                opt:'+',
                result:0
            },
            methods:{
                ccc:function(){
                    switch(this.opt){
                            case '+':
                            this.result = parseInt(this.n1)+parseInt(this.n2)
                            break;
                            case '-':
                            this.result = parseInt(this.n1)-parseInt(this.n2)
                            break;
                            case '*':
                            this.result = parseInt(this.n1)*parseInt(this.n2)
                            break;
                            case '/':
                            this.result = parseInt(this.n1) / parseInt(this.n2)
                            break;  
                    }
                }
            }
        })
    </script>
</body>
</html>